Abstract: The power driving shaft of helicopter is the hub between the engine and the decelerator. A lot of tests are required for the development of power driving shaft, which need running for a long time at high speed、high torque and large deflection angle. Aiming at the problem of short life of the test device, according to the test principle, this paper analyzes the fault of the original test device. Using dynamic design and modal simulation, the structure of the test device has been greatly improved. According to the test, the improved test device works stably and reliably, and its life is increased from 20 hours to 1000 hours.